This application claims the priority of Korean Patent Application Nos. 10-2004-0103072 filed Dec. 8, 2004 and 10-2005-0042421 filed May 20, 2005 in the Korean Intellectual Property Office, the disclosure of which are incorporated herein in their entirety by reference.
1. Field of the Invention
The present invention relates generally to an optical transmission technology for optical communication, and more particularly, to a system for retiming, reshaping, and reamplifying (3R) regeneration of an optical signal.
2. Description of the Related Art
Signal distortions inevitably occur in optical communications. Thus, for example, the signal strength of an optical signal propagating in an optical medium such as an optical cable will be reduced in strength, and its waveform may be temporally deformed or transformed in shape due to dispersion. Such distortion affecting the optical signal in an optical communication system can be removed by performing retiming, reshaping, and reamplifying (3R) regeneration. Because a 3R regeneration system is capable of restoring a distorted optical signal substantially to its original form, it is considered indispensable when forming an optical network.
Of the 3R, the “retiming” or clock regeneration refers to extracting a clock signal from a distorted optical signal and reproducing via a decision circuit an optical signal that is basically in its form before distortion. The clock signal extraction can be performed by a technique utilizing an electrical phase locked loop (PLL) circuit or full optical regeneration technique; however, the clock signal extraction utilizing an electrical PLL circuit will be restricted in the processing speed.
The conventional 3R regeneration technique uses a separate clock regeneration element coupled to a separate decision element. This will inevitably lead to coupling loss due to coupling of the clock regeneration element and the decision element, and, further, the conventional 3R regeneration system utilizing these separate elements will result in a rather complex system as it will require additional elements for adjusting the polarization and delay of the optical signal.
To solve the problems associated with couple loss, some conventional technique proposes a monolithically integrated technology. U.S. Pat. No. 6,208,454 proposes a Mach-Zehnder wavelength converter integrated with an integrated distributed feedback (DFB) function or a tunable laser diode. This conventional monolithically integrated technology is reportedly considered useful for high-speed operations owing to somewhat low coupling loss; however, it is not shown to produce results for wavelength conversions of more than 10 Gbps due to problems of surface reflection and others. Thus, no conventional technique has produced acceptable results in producing a functioning monolithically integrated 3R regeneration system.